Warmest springs on record bring earliest flowers ever

This viola is one of many plants flowering earlier than when long-term observations began with Henry David Thoreau and Aldo Leopold.

By John Roach, NBC News

During the exceptionally warm springs of 2010 and 2012, plants bloomed earlier in the eastern U.S. than they have since the American writer and naturalist Henry David Thoreau started keeping records near Walden Pond in 1852.

Many plants now flower several weeks earlier than they did in the 19th century, a response linked to increasingly warmer springs due to global climate change.

For example, in Massachusetts, plants are flowering 20 days earlier now than they were during Thoreau’s time. In Wisconsin, where data on flowering dates was recorded by environmentalist and writer Aldo Leopold in the 1930s, flowering dates are, on average, 24 days earlier.

So far, plants are adjusting to the earlier flowering without any major complications. But scientists are concerned a shortened winter will rob them of the time they need to undergo the physiological changes that allow them to reproduce come spring.

To find out if this threshold was near, Harvard University evolutionary biologist Charles Davis and colleagues turned to the warmest two springs in the eastern U.S. on record. In Massachusetts, where Walden Pond lies, plants flowered on April 24 in 2010 and April 25 in 2012. They did just fine.

"My fear is that people will see, like wow, there is some built-in resiliency here that was unexpected — namely that plants are able to continue to push their flowering times earlier with warming temperatures," Davis told NBC News.

"But I think the jury is still out on whether or not this is clearly a good or clearly a bad thing."

The concerns are many. An earlier flowering date raises the odds that a late spring frost will kill the flowers before they have a chance to attract the birds and bees needed for pollination and reproduction.

Richard Primack / Boston University

A pink lady's slipper orchid is among the earlier flowering plants.

If the birds, bees and other insects can’t pollinate the flowers, the creatures that eat the pollinators too will run into a lack of food.

Earlier flowering plants also mean an earlier start to the cycle of plants taking up and transpiring water and absorbing carbon dioxide from the atmosphere via photosynthesis, and turning it into plant biomass.

"You end up with the whole ecosystem being affected," Libby Ellwood, a biologist at Boston University and co-author of a paper describing the finds published online Wednesday the journal PLoS One, told NBC News.

She expects there will be some winners and losers due to the earlier flowering. For example, some plants may take good advantage of a longer growing season, but might also have a greater chance of being impacted by drought.

A particular charm of the study comes from its dataset stretching back to records of Thoreau and Leopold, noted the researchers.

Without their data, the context for how much the flowering dates have changed in recent years would be lost.

What’s more, the length of the dataset allowed the researchers to create a model that predicts a plant's response to warming temperatures. Plug in a temperature variable and out comes a range of possible flowering dates. “These recent years fell into that equation,” noted Ellwood.

Davis, too, sees the charm in the data.

“In a funny sort of way, Thoreau and Leopold are being acknowledged as modern climatologists,” he said.

John Roach is a contributing writer for NBC News. To learn more about him, check out his website.